T/undo 2

src/datacontroller.js

@@ -171,7 +171,8 @@ export default class DataController {
 		const modelRoot = this.model.getRoot( rootName );
 
 		this.model.enqueueChanges( () => {
-			this.model.batch()
+			// Initial batch should be ignored by features like undo, etc.
+			this.model.batch( 'transparent' )
 				.remove( ModelRange.createFromElement( modelRoot ) )
 				.insert( ModelPosition.createAt( modelRoot, 0 ), this.parse( data ) );
 		} );

src/model/batch.js

@@ -35,27 +35,51 @@ export default class Batch {
 	 * Creates Batch instance. Not recommended to use directly, use {@link engine.model.Document#batch} instead.
 	 *
 	 * @param {engine.model.Document} doc Document which this Batch changes.
+	 * @param {'transparent'|'default'} [type='default'] Type of the batch.
 	 */
-	constructor( doc ) {
+	constructor( doc, type = 'default' ) {
 		/**
-		 * Document which this Batch changes.
+		 * Document which this batch changes.
 		 *
-		 * @member {engine.model.Document} engine.model.Batch#doc
 		 * @readonly
+		 * @member {engine.model.Document} engine.model.Batch#doc
 		 */
 		this.doc = doc;
 
 		/**
-		 * Array of deltas which compose Batch.
+		 * Array of deltas which compose this batch.
 		 *
-		 * @member {Array.<engine.model.delta.Delta>} engine.model.Batch#deltas
 		 * @readonly
+		 * @member {Array.<engine.model.delta.Delta>} engine.model.Batch#deltas
 		 */
 		this.deltas = [];
+
+		/**
+		 * Type of the batch.
+		 *
+		 * Can be one of the following values:
+		 * * `'default'` - all "normal" batches, most commonly used type.
+		 * * `'transparent'` - batch that should be ignored by other features, i.e. initial batch or collaborative editing changes.
+		 *
+		 * @readonly
+		 * @member {'transparent'|'default'} engine.model.Batch#type
+		 */
+		this.type = type;
+	}
+
+	/**
+	 * Returns this batch base version, which is equal to the base version of first delta in the batch.
+	 * If there are no deltas in the batch, it returns `null`.
+	 *
+	 * @readonly
+	 * @type {Number|null}
+	 */
+	get baseVersion() {
+		return this.deltas.length > 0 ? this.deltas[ 0 ].baseVersion : null;
 	}
 
 	/**
-	 * Adds delta to the Batch instance. All modification methods (insert, remove, split, etc.) use this method
+	 * Adds delta to the batch instance. All modification methods (insert, remove, split, etc.) use this method
 	 * to add created deltas.
 	 *
 	 * @param {engine.model.delta.Delta} delta Delta to add.
@@ -81,7 +105,7 @@ export default class Batch {
 }
 
 /**
- * Function to register Batch methods. To make code scalable Batch do not have modification
+ * Function to register batch methods. To make code scalable Batch do not have modification
  * methods built in. They can be registered using this method.
  *
  * This method checks if there is no naming collision and throws `batch-register-taken` if the method name

src/model/delta/basic-transformations.js

@@ -230,10 +230,19 @@ addTransformationCase( UnwrapDelta, SplitDelta, ( a, b, isStrong ) => {
 	// If incoming unwrap delta tries to unwrap node that got split we should unwrap the original node and the split copy.
 	// This can be achieved either by reverting split and applying unwrap to singular node, or creating additional unwrap delta.
 	if ( compareArrays( a.position.path, b.position.getParentPath() ) === 'SAME' ) {
-		return [
+		const transformed = [
 			b.getReversed(),
 			a.clone()
 		];
+
+		// It's a kind of magic-magic-magic-maaaaagiiic!
+		transformed[ 1 ].operations[ 1 ].targetPosition.path[ 0 ]++;
+		// But seriously, we have to fix RemoveOperation in the second delta because reversed UnwrapDelta creates
+		// MergeDelta which also has RemoveOperation. Those two operations cannot point to the same "holder" element
+		// in the graveyard, so we fix it by hand. This is the only case where it happens in "special" transformation
+		// cases, and it won't happen for "default" transformation apart of RemoveDelta, where it is okay.
+
+		return transformed;
 	}
 
 	return defaultTransform( a, b, isStrong );

src/model/document.js

@@ -108,10 +108,12 @@ export default class Document {
 		/**
 		 * Document's history.
 		 *
+		 * **Note:** Be aware that deltas applied to the stored deltas might be removed or changed.
+		 *
 		 * @readonly
 		 * @member {engine.model.History} engine.model.Document#history
 		 */
-		this.history = new History();
+		this.history = new History( this );
 	}
 
 	/**
@@ -159,7 +161,10 @@ export default class Document {
 
 		this.version++;
 
-		this.history.addOperation( operation );
+		if ( operation.delta ) {
+			// Right now I can't imagine operations without deltas, but let's be safe.
+			this.history.addDelta( operation.delta );
+		}
 
 		const batch = operation.delta && operation.delta.batch;
 
@@ -172,10 +177,11 @@ export default class Document {
 	/**
 	 * Creates a {@link engine.model.Batch} instance which allows to change the document.
 	 *
+	 * @param {String} [type] Batch type. See {@link engine.model.Batch#type}.
 	 * @returns {engine.model.Batch} Batch instance.
 	 */
-	batch() {
-		return new Batch( this );
+	batch( type ) {
+		return new Batch( this, type );
 	}
 
 	/**